The disclosure relates to a hydrostatic drive which is provided in particular for starting an internal combustion engine, in particular a diesel engine.
The hydraulic machine of a hydrostatic drive of this type is driven as a pump by an internal combustion engine which is generally a diesel engine. In the mode as a pump, the volumetric flow of pressure medium is supplied, for example to a hydropneumatic high pressure accumulator, which is also called hydraulic accumulator for short, or to other hydraulic consumers. The drive can be arranged on a mobile working machine, such as, for example, an excavator, and the other hydraulic consumers can be, for example, a hydraulic steering system and various lifting cylinders.
Documents U.S. Pat. No. 3,384,027 and DE 20 2013 003 490 U1 show drives of this type, in which the hydraulic machine apart from supplying other hydraulic consumers, also charges a hydraulic accumulator. After a stoppage of the internal combustion engine, for the restarting thereof, the hydraulic machine is operated as a motor and is supplied with pressure medium from the hydraulic accumulator.
Aspects of fuel saving have become increasingly important in recent years, and therefore there are approaches for start-stop functions for the diesel engine. If the latter is not required, it is intended to be switched off, and when it is required again, it has to be restarted. This may take place comparatively frequently, with energy being required for each start.
Document WO 2012/125798 A1 shows a drive in which the internal combustion engine in the normal mode drives a hydraulic machine which is operated as a pump and which—in addition to supplying other hydraulic consumers—also charges the hydraulic accumulator. For restarting of the internal combustion engine, the pressure medium of the hydraulic accumulator is used in order to drive the hydraulic machine, which is then used as a starter motor. For a transitional period in this case, a consumer shut off valve in the pump line to the other consumers is closed so that the latter are not activated or moved in an uncontrolled manner.
A disadvantage of drives of this type is that, when the hydraulic machine is used as a starter motor, the throughflow direction has to be maintained so that the internal combustion engine is started again in the same predetermined direction of rotation at which it has previously operated. The connection which, in the normal mode, was the low pressure connection or intake connection of the hydraulic machine acting as a pump therefore, upon starting, has to form the high pressure side of the hydraulic machine acting as a motor. Accordingly, the drive from WO 2012/125798 A1 requires various selector valves, for which it has to be ensured that they are switched before the internal combustion engine can be started.
By contrast, the disclosure is based on the object of providing a hydrostatic drive for starting an internal combustion engine, in which the internal combustion engine can be started without a pressure side on the hydraulic machine having to be changed in comparison to the mode as a pump. The start-stop function is intended to be able to react rapidly and reliably here.
This object is achieved by a hydrostatic drive having the features of the disclosure.
Further advantageous refinements of the disclosure are described in the dependent claims.